This invention relates to vacuum servo booster devices such as vacuum servomotors or the like, which are particularly adapted for use in hydraulic braking system of a vehicle.
Conventional vacuum servomotors comprise a housing defined by a front shell and rear shell, a valve body slidably supported by the rear shell and incorporating therein a valve mechanism, a flexible diaphragm connected to the circumference of the valve body and extending in the radial direction toward the circumference of the housing so as to divide the interior of the housing into a front chamber and a rear chamber, and a piston plate mounted on the valve body and extending contiguous to the diaphragm. When a vacuum servomotor of the aforesaid kind is used in a vehicle hydraulic braking system, a master cylinder is rigidly secured to the front shell by means of bolts or the like, and the rear shell of the servomotor is rigidly connected to a toe-board (a plate partitioning a driver's compartment from an engine) in accordance with usual practice. In such a case, the housing of the servomotor must receive the force acting on the master cylinder. When the strength and rigidity of the housing of the servomotor are insufficient, there have been problems such that the housing of the booster is deformed, or that the effective stroke of the booster or the master cylinder is reduced, or the like.
It is possible to overcome these afore-mentioned problems by increasing the cross-sectional width of the shells which constitute the housing, however, this solution creates problems such that the weight of the booster increases and that the amount of the material needed for fabricating the housing also increases.